Fabric conditioners are commonly used to deposit a softening compound onto a fabric. Typically, such compositions contain a water-insoluble quaternary ammonium fabric softening agent dispersed in water at a level of softening agent up to 7% by weight, in which case the compositions are considered dilute, or at levels from 7% to 30% by weight, in which case the compositions are considered concentrates.
Fabric conditioning super concentrates can be provided which have in excess of 30% by weight fabric conditioner. However, such compositions need to be diluted upon use.
One of the problems associated with dilute and concentrated fabric softening compositions is the physical instability of such compositions when stored. Physical instability manifests itself as a thickening on storage of the compositions to a level where the composition can no longer be poured and can even lead to the formation of a gel which cannot be redispersed. This problem is accentuated by having a concentrated composition and by storage at low or high temperatures. With concentrated compositions comprising biodegradable ester-linked quaternary ammonium compounds, the problem of physical instability is more acute than with compositions comprising traditional quaternary ammonium compounds not having any ester links.
Conventional dilute fabric conditioners frequently contain an electrolyte such as calcium chloride to maintain the formation in a pourable condition. However, the formation of a stable concentrated product is not so easily achieved. The viscosity, pourability and flowability characteristics of conventional fabric conditioners are not maintained if the level of cationic softening active exceeds 8% by weight of the composition, even in the presence of calcium chloride. In such concentrated systems, phase separation or gelling occurs when the level of cationic softening agent exceeds 8% by weight.
EP-A-0409502 in the name of Unilever PLC discloses fabric softening compositions which comprise biodegradable quaternary ammonium compounds, which compositions are of acceptable stability. They contain a C8-C28 fatty acid material or salt thereof. The weight ratio of quaternary ammonium material to fatty acid is in the range 10:1 to 1:10.
WO 89/11522 in the name of Henkel KGaA discloses liquid laundry-conditioning agents containing quaternary ammonium compounds in combination with fatty acid in a ratio of 10:1 to 1:3. The compositions have acceptable stability and give good absorbency to textiles treated with them. The ratio of quaternary ammonium material to fatty acid is in the range 10:1 to 1:3.
EP-A-0122141 in the name of Unilever PLC discloses a liquid fabric softening composition containing a water soluble cationic fabric softener, a nonionic material of specified HLB and an electrolyte. The compositions have improved viscosity stability. The nonionic material may include C8-C24 fatty acids. Biodegradable quaternary ammonium material is not specifically mentioned. The ratio of quaternary ammonium material to nonionic material is less than 5:1.
Although general stability is approached in EP-A-0409502 and WO 89/11522, they do not deal with the specific problem of providing viscosity which is stable over time in fabric softening compositions comprising biodegradable quaternary ammonium material. Accordingly, the present invention sets out to provide fabric softening compositions comprising less than 30% by weight of a biodegradable quaternary ammonium material with improved viscosity stability characteristics.
The present inventors have discovered that surprisingly improved viscosity stability characteristics can be obtained in such compositions if a relatively small quantity of unsaturated fatty acid is used as a viscosity stabiliser.